Manufacture of synthetic rubber



Patented July 5, 1949 j UNITED srrs ATENT OFFICE 2,474,807 MANUFACTURE OF SYNTHETIC RUBBER Dwight L. Schoenc, Naugatuck, Conn, assignor to United States Rubber Company, New York,

. Y, a corporation of New Jersey No Drawing. Application December 4, 1946, Serial No. 713,907

8 Claims. (01. 260-80.7) This invention relates to improvements in the or they may be added to a synthetic rubber commanufacture of synthetic rubber, and particupound prior to complete or final polymerization larly to improvements in the physical properties at a later stage in the polymerization process so of utadienes-l,3 and of mixtures of butad1enes- 5 terpolymerlzlng or chemically combining the 1,3 with compounds which are copolymerlzable. divinyl benzene ith the other synthetic rubber It is known that in the manufacture of pro constituent or constituents. ducts from synthetic rubbers, such as commercial Synthetic rubber latex such as an aqueous GR-S rubber which is a copolymer of butadieneemulsion of butadiene-1,3 with styrene (GR-S 1,3 and styrene, considerable shrinkage takes latex) normally exhibits considerable shrinkplace during milling, breaking down and comage after coagulation and during dr and V pounding the raw material P110 to vclemra ni a wn Thls property 1s particularly und on and during vulcanization This shrinkage sirable 1n the manufacture of sponge rubber from introduces diflicultles into the accurate measurea foam of synthetic latex It is known that mament of freshly m lled stocks, causes excessive turmg such rubber latex with sulfur, as by letsurface roughness or rugoslty 1n calendered colnting the latex stand for 30 hours with 1% by pounds as well as irregular and broken edges, and Weight of sulfur based on the rubber solids congives rise to variations in thickness when the tent has the e fect of r du in th hrinka f compound is extruded. the wet sponge after the rubber sponge has gelled,

According to the present invention, there is but t required long periods f time av c added to the polymerizable materials in the preptain practical disadvantages. The present inarat10n of synthetic rubber, prior to final poly- Ventlon eliminates the necessity for long maturmerization, a small amount of a divinyl benzene, ins p riods and the polymerizable compounds napthalene or diphenyl or a di(ot-methyl) vinyl such as divinyl benzene may be conveniently inor di-(a-ethyl) vinyl homologue thereof. These corporated in the latex prior to final emulsion compounds conform to the general formula: polymerization of the rubber-forming monomers.

cess of .5% based on the rubber polymer content 1 n have the desired elfect of maintaining surface Where A may be an aryl nucleus such as n v ingly, as shown in the examples below, the tensile as to render the virtually worthless for use zone, m-divinyl benzene, p-divinyl benzene, 1,2- Th present 1 divinyl naphthalene, 1,4-divinyl naphthalene, any of th s a 1,8-divinyl naphthalene, o-di-isopropenyl benization zene, p-di-(a-ethyl vinyl) benzene, 4, l-divinyl Oxide initiated aqu ivin l be ut a y f t above pounds, 40 polymerization thereof initiated by metallic sosodium hydride or organo sodium compounds, thereby yielding a polymer in which the The compound having the above general formonomers are believed to form a net-work or gelmula is mixed in small quantities with the synlike structure of polymer chains. e c rubber ingredients prior to the final Stage xal'nples of synthetic rubber-producing polyof polymerization, and polymerization is carried merizable materials which are improved by the out in the customary manner according to known present invention are the butadienes-LS such as practice, at least part of the polymerization being butadiene-L3, Z-methyl-butadiehe-LS (isoprene), performed in the presence of a small quantity of 2,3-dilnethy1-butadiene-1,3, piperylene, Z-chloro- :he compound. The compound, for example, butadiene-LS (chlorop-rene) and mixtures thereof livinyl benzene, may be added to the synthetic and mixtures of such butadienes-l,3 with other ubber ingredients at the initial stage of mixpolymerizable compounds which are capable of are of the monomers in amounts between0.01 and forming rubbery copolymers with butadienes-LB, .5 parts by weight based on. 100*parts of total for example, up to 70% by weight of such mixture mthetic ru-bbercontent as exemplified below, of compoundswhich have a single C=C double :51am... ..c.

linkage, for example, esters of maleic and iumaric acids, or compounds which contain a single group where at least one of the disconnected -valences is attached to an electro-active group,

i. e., to a group which substantially increases the electrical dissymetry or polar character of the molecule. Examples of compounds which contain a single group and are copolymerizable with butadienes- 1,3 are the aryl olefines, such as styrene,- vinyl naphthalene, 0-, m-, or p-monochlorostyrene; the alpha methylene carboxylic acids and theirv esters, nitriles and amides, such as acrylic acrylate, methyl methacrylate, methacrylonitrile, methacrylamide;- isobutylene;

Vinylacrylonitrile,

EXAMPLE I Test-samples of GR-S synthetic rubber containing varying amounts of divinyl benzene. were made up according to the formulations listed in the table below, the-figures representing parts by weight. Each sample was separately prepared and then polymerized by heating in a closed reactor for 14 to 16 hours at,.50 C. The reaction was stopped by theaddition -of O.1 part of hydroquinone and the unreacted monomers were removedin conventionalmanner, by venting off the butadiene--1,3, and. steam-distilling the styrene. The percentage, of-conversion oi the monomers to polymers is also indicated in the table, and itwill be noted that test sample F is a standard .GR-S rubber containing no divinyl benzene.

Test Sample Ingredients C D F 1 Butadiened, 3 72 72 72 Styrene 27.8 27. 5 28 Divinyl benzene 0. 2 0. 5 0 Dodecyl mercaptan.... 0.6 0.16 0. 6 Potassium persulfatcu 0. 3 0.3. 0.3 Soap 5. 0 5. 0 5. 0 Water 180 y 180 V 180 Percent Oonversion. 77 78 77 1 Standard.

acid, methyl The dodecyl mercaptan is. a conventional polye5 merization regulator and the potassium persuli ate is a conventional catalyst. The emulsions thus produced in latex form were then treated separately by addition of a commercial ketonediarylamine antioxidant and then were flocculated with salt-acid and dried at 55 C. The finished polymersamples were then compounded according to the following. formulae, after which portions of, eachof'thetest sample compounds were subjectedyto vulcanizationfor-different p efor about 5 hours. At

riods of time, i. e. 30, 60, and minutes. Parts are listed by weight.

Test Sample Compounding J Ingredients 1 A B O D E F I GR-S rubbcrx. 100 100 100 100 100 Channel black. 50 50 50 50 50 Zinc oxide 5 5 5 5 5 5 Goal tar softener 5 5 5 5 5 5 Sulfur 2 l. 25 1. 25 1. 25 l. 25 2 Mercaptobenzothiazole. 1. 5 1. 5 1. 1. 5 1. 5 1. 5

fs The compounded test samples were subjected to a series of comparative physical tests. Sample F is the standard GR-S material containing no divinyl benzene and samples A to E containing varying amounts of divinyl benzene were compared therewith.

Calender shrinkage test Samples of the materials A to F were tested for calender shrinkage as. described in an article by White et al. published in Industrial and Engineering Chemistry, vol. .37, (.1945) page 76.7. Dimehsionally identical. strips of each of the samples were calendered under identical temperature conditions from stocks A to F'and their length was measured as they left the calender nip. The samples were then allowed to cool and shrink freely for 8 hours, after. which the. length was again measured for each sample. The figures expressed below represent the original length less the length afterv shrinkage, divided by the original length: in other words, the percentage of shrinkage.

Sample A B C D n F Per Cent Shrinkage 30 21 20 i 5 5 43 Reference to the composition; of. the various samples shows that as the divinyl benzene content is raisedgradually to 1 percent the calender shrinkage is reduced. Samples D and E,. containing respectively 0.5% and, 1.0% of divinyl benzene, both exhibited only 5% calender shrinkage as compared with sample F which shrank 43%. Samples A, B, and C all shrank considerably less than sample F.

Rugosity .test

sample F.

Sample A B- I F Rugosity value .Q

Tubing swell test Samples of each .ot'the stocks A top were extruded througha triangulan die irr-a tubing machine as, describedby Nellen in; Industria and Engineering Chemistryfl. vol. 29-,-- 1937i pagl 886, andthe samples were: permitted tostam the; end .ot the standim sectional shrinkage to sample F; sample D exhibiting the optimum.

Sample A B C D E F Per cent swell 33 26 25 4 5 49 Twoseries of tests were run on samples A to F to determine their tensile strength: one on unaged stock, the other on stock which was aged for 96 hours at 100 C. prior to vulcanization. The vulcanization or curing time is stated for eachmeasurement, as shown below, and curing was at 45 lb. steam pressure.

Tensile strength test The following figures represent the pounds per square inch which were applied when the various samples were stretched to the breaking point. Samples of each of the compounds A to F were cured for the periods indicated, and comparative results with both unaged and aged samples are shown:

Pounds per Sq. Incl1-Unaged Stock Samples Curing time A B O D E F 30 minutes 1, 980 2, 000 1,500 600 250 1, 800 60 minutes 2, 610 2, 600 2, 240 960 2, 920 90 minutesm"- 2,450 2, 590 2,180 1, 150 2, 800

Pounds per Sq. Inch-Aged Stock Samples A B C D E F 30 minutes 2, 550 1,850 2, 200 1, 350 1, 310 60 minutes 2, 210 2 250 2, 250 1,350 90 minutes.... 2,400 2 370 2,200 1,400 2, 430

The blank figures for sample E (containing 1.0% divinyl benzene) indicate that these samples were too weak to be removed from the curing molds in one piece and hence could not be tested.

Elongation test elongation of the various samples in the preceding test at the breaking point.

As in the Tensile strength test above, all the samp1es,c0ntaining 1%, divinyl benzene (sample The following figures represent the percent E) were too weak tobe removed in one piece from the molds, except the unaged stock which was cured for 30 minutes and which broke after elongation of 130%.

EXAMPLE II Blends of sample stocks were made up, by milling together stocks similarto sample D and sample F of Example I. Sample G was made by blending equal parts of samples D and F. Sample H was the result of blending one part of sample D with three parts of sample F. Sample J was similar to the standard sample F, except that it was milled to an extent equivalent to the milling of the blended samples G and H in order to place the tests on a comparative basis. Various tests were performed as in Example I, and the results are tabulated below. Each sample was compounded with 2.0 parts sulfur and the other compounding ingredients were milled into the stocks as in Example I. In Example II, all stocks were unaged.

1 Standard.

The results of the tests on the blended samples (sample G containing an aggregate of 25% divinyl benzene based on the polymer weight and sample H containing an aggregate of divinyl benzene) show improved rugosity and reduced calender shrinkage and reduced tubing swell over the standard sample J, while the strength figures for the blends are entirely adequate for commercial use.

In view of the many changes and modifications that may be made without departing from the principles underlying the invention reference should be made to the appended claims for an understanding of the scope of protection afforded the invention.

Having thus described my invention, what I claim and desire to protect by Letters Patent is:

1. Synthetic rubber comprising a polymerizate of a polymerizable mixture of monomers selected from the group consisting of butadiene-1,3, isoprene, 2-chl0ro-butacliene-l,3, 2,3-dimethyl butaoliene-1,3, and piperylene, and mixtures of such butadienes-1,3 with up to 70% by Weight of such mixture of material which has a single group and is copolymerizable with butadienes- 1,3, together with .01 to .5 percent by weight of a compound having the general formula R R CH2=(|3-A :CH:

where A represents a member of the group consisting of phenylene, naphthylene and diphenylene and R represents a member of the group consisting of hydrogen, methyl and ethyl.

2. Synthetic rubber comprising a polymerizate of a mixture of a major proportion of butadienecontains; a. singles.

1,3 ia'nda minor proportion :of 'au-compound which group and is copolymerizablewith butadiene 13 and .01 to .5 percent by weight of divinyr-benzene.

4. Synthetic rubber comprising a zpolyrnerizate of a mixture of:a major proportion of butadiene- 1,3,. anda minor proportion of styrene and ;0'1 to .5 per. cent by weight .of vdivinyl benzene.

5. In the process of polymerizing .an aqueous emulsion of polymerizahle "monomers compris- :ing a major proportion of butadienev-;1;,'3.- and a minor proportion of a compound. whieh' oonta'ins a single .CHFC/ group and is copolymerizable with butadienea'lfi, the. step which comprises performing at least. a part of theipolymerization in the presence 201.101 to .5 percent based-on the weight of .polymer-izia,..- ble material of a compound having the general formula.

where A represents a member of the group consisting of phenylene, naphthylene and (ii-phenylene and'Ri represents a member of thegroup consisting of hydrogen, methyl and ethyl.

6.111 the process of polymerizing an aqueous.

emulsion of poly'merizable monomers comprising a major proportion of buta'cl-iene-L3 "and a minor proportion of a compound which contains a single group and is r-copolymerizable.with ihutadienelj,

the-'s'teprwhich comprisesperiorming .at least-a :Lthe- .polymerization in the presence. of percent based ion .the weight of polymer;- izahiemateria214of.:.divinyl benzene;-

.="lin.z the. .pro'cessaof polymerizing an aqueous emulsion of. pol-ymerizable monomers. selecteii from thewgroup. persisting wo f. hu-taciienee1,3, :iso" pee-ne 2eehloroebutadiene- 13', 2,3 :dimethyl butadime-9L3, andIpiperyIe-nazand mixtures-of such hutadienes-LB withup. to 70% .by weightofsuch mixture of material whicnfhas-a single.

group and is copolymerizable with butadienesli3 thestep which vcomprises performing at least apart. of the .pelymerizationpin the presence of .01 to. 45 percent based on th w i htof polymerizable.material of a compound 'hayingthe. general formula.

s where A represents a member of the group consisting::ofphenylene;.naphthylene and-.diphenyl- .ene anciv It represents a member of the group eensis inem hy rogemmethylzand ethyl.-

8.Tl18. processeof vmakingw synthetic rubber whiehxeomnrises; polymerizing. 1a mixture-ref mon emer -comprising La m.aior .ipr pjortion of. butae dime-1,3 and a minor proportion of styrene in the .presenceiof ..01 .to .5 vpercentof divinyl benzene...

' DWIGHT .L. SCHOENE.

REFERENCES omen K The .ifolloiwing referemces are of record the file of this patent:

UNITED STATES PATENTS Number... Name Date 1,901,354 Meisenburg Mar. 14, 1933 1915,5 45... Meisenburget a1. June 27, 1933 1,938,731 'Tschunkuret al.. Dec. 12,1933 1 9381.751 M'eisenburg et a1. Dec. 12,1933 2,066330 Carothers et a1 Jan. 5,1937 2,089,444 Staudinger et a1; Aug. 10, 1937 '2',-418,-9F78'=' Mertens Apr. 15-, 1947 Schoene et ail, :Deve1opmentof a better processing GRFS, Ind;- Eng-1, Chem. Ind. ECL, Dec. 1946, pages 1246-1249.

India Rubber'world', June 1946, page 365.

India 'R ubber world; August 1946; page 680. 

